let n = new Number(readline())

function jump(n) {
  if (n == 1) return 1
  if (n == 2) return 2
  let ni = 1
  let nj = 2
  let nk = ni + nj
  for (let i = 3; i <= n; i++) {
    nk = ni + nj
    ni = nj
    nj = nk
  }
  return nk
}
print(jump(3))
function print(val) {
  console.log(val);
}

function readline() {
  return '1'
}